Exemplary embodiments of the invention relate to a piston arrangement for a combustion chamber of an internal combustion engine having a variable compression ratio.
German patent document DE 33 46 967 C2 discloses a plunger piston having variable compression height for internal combustion engines, in which the piston crown is arranged in a relatively axially displaceable manner with at least one part of the piston ring section on the lower part which accommodates the piston pin. In the plunger piston, two interconnected chambers are provided which can be filled with pressure oil, and the respective volumes of which change with respect to one another in reciprocal proportion upon relative displacement of the piston crown, and of which a first chamber as control chamber lies directly below the piston crown, while a second chamber as damping chamber is arranged below the control chamber. Furthermore, in the piston, the pressure oil is conducted via valves, of which one is designed as a pressure limiting valve and is arranged between the control chamber and a space that is open towards the crankcase. The damping chamber is arranged in a divided manner in the interior of the piston and is delimited by a shoulder emanating from the center of the piston crown, a central recess in the piston lower part is provided for engaging with the shoulder engages, a collar of the piston lower part projects radially into the recess at the piston-crown-side end of the recess and which separates the two chambers from one another, and a sealing washer can be detachably fastened to the shoulder and which is held by a screw screwed to the shoulder.
A device for controlling the oil feed into a control chamber of the piston having variable compression height for internal combustion engines is disclosed in German patent document DE 36 38 783 C2. The control chamber is arranged between an inner piston part and an outer piston part that is displaceably guided thereon. The control chamber is connected to the lubricating oil circuit of the internal combustion engine via an oil hole, which is arranged in the inner piston part and in the course of which a non-return valve that opens in the direction towards the control chamber is fitted. The oil hole opens into an oil groove in a small-end bushing of the connecting rod articulated to the inner piston part via a hollow piston pin which forms an oil storage chamber, and via a longitudinal oil hole having a control oil groove and extending from the oil groove through the shaft of the connecting rod supported by a connecting rod bearing, and a transverse hole extending in the crank pin between the control oil groove and a main oil hole.
Here, the connecting rod bearing contains the control oil groove across part of the circumference thereof arranged in such a way that the transverse hole overlaps the control oil groove in the region between the last third of the piston outward movement to the last third of the piston inward movement.
Moreover, a piston for an internal combustion engine having a variable compression ratio is known from German patent document DE 10 2009 048 172 A1. The piston comprises a first piston part and a second piston part coupled movably relative to one another, forming at least one first chamber, to which a pressure medium, in particular a pressure fluid, can be supplied, and the volume of which is variable. Here, at least one control valve device is arranged internally on a piston skirt of the piston, by means of which a volume of the pressure medium in the first chamber can be adjusted.
For a reciprocating piston engine, in particular an internal combustion engine, having a device for changing the piston stroke function, it is proposed in German patent document DE 197 57 871 A1 to attach to the cylinder block, in the vicinity of the piston or of the connecting rod, an electrical coil, which is not moved by the crank drive and between which and an oscillating component moved by the crank drive a force action can be produced at least cyclically corresponding to the movement of the crank drive. The force action can be produced directly via an electromagnetic field or indirectly by mechanical contact, wherein, due to the force action of the coil, a connecting link is displaced into the interior or in the interior of the cylinder barrel such that same cyclically comes into contact with the component moved by the crank drive. The device for changing the piston stroke function can be controlled or the adjustment state thereof detected due to the force action.
Japanese patent document JP 60 142020 A likewise discloses an internal combustion engine having a piston, a piston pin and a connecting rod in a cylinder, wherein the piston pin is designed at least partially eccentrically in the length thereof and can be moved by means of a control element into at least two positions and, thereby, the compression ratio of the cylinder of the internal combustion engine can be changed.
It has been shown that adjustments of the piston height of this kind and therefore of the compression ratio are intricate.
Exemplary embodiments of the present invention are directed to a piston arrangement for a combustion chamber having a variable compression ratio, by means of which a simple variable adjustment of the compression ratio of the combustion chamber is made possible.
Such a piston arrangement for a combustion chamber having a variable compression ratio, in particular cylinder, of an internal combustion engine which is designed, in particular, as a reciprocating piston internal combustion engine, in particular of a motor vehicle, includes a piston and a device for the variable adjustment of the compression ratio associated with the combustion chamber. Furthermore, the piston arrangement includes a piston pin. The piston pin is coupled to the piston via respective connecting regions. Here, the piston pin is accommodated, for example, at least in some areas, in accommodating openings, in particular passages, of the piston. The piston can be coupled to a connecting rod of the internal combustion engine, in particular in an articulated manner, via the piston pin.
The piston can be coupled in an articulated manner to a crankshaft of the internal combustion engine via the piston pin and the connecting rod such that translational movements of the piston in the combustion chamber relative thereto can be converted into a rotational movement of the crankshaft.
According to the invention, the device includes the piston pin. Here, the piston pin has at least one eccentric element, which is eccentrically arranged with respect to the connecting region of the piston pin and via which the piston can be coupled to the connecting rod. If the piston pin is coupled to the connecting rod via the eccentric element and if the piston pin is rotated relative to the connecting rod about the longitudinal central axis of the eccentric element, which is designed at least substantially in the form of a right circular cylinder, and relative to the piston about the longitudinal central axis of the at least one connecting region of the piston pin, which is designed at least substantially in the form of a right circular cylinder, then, as a result of the eccentric arrangement of the eccentric element relative to the connecting region of the piston pin, the rotation of the piston pin relative to the connecting rod and relative to the piston causes the piston arranged in the combustion chamber to be moved, in particular displaced, relative to the connecting rod in the direction of the longitudinal extension thereof.
This is accompanied by a change in the distance between the piston and the axis of rotation of the crankshaft. Furthermore, this is accompanied by a change in the distance between the piston and a combustion chamber roof of the combustion chamber. Thereby, the compression ratio of the combustion chamber is changed. The change in the compression ratio is implemented here in a particularly simple and therefore cost-effective and installation-space-effective manner.
Moreover, by means of the piston arrangement according to the invention, it is possible to adjust the compression ratio as required and to suit different operating points of the internal combustion engine. The internal combustion engine can therefore be operated efficiently and with only a small energy consumption, in particular fuel consumption. Further, the piston arrangement is not only highly compact but also has a very high proportion of identical parts compared with a conventional piston arrangement that does not allow the compression ratio to be adjusted. This results in low costs.
In an advantageous embodiment of the invention, the device includes at least one control element. Here, the control element can be moved on the piston relative to the piston and relative to the piston pin between at least two positions. In particular, the control element can be displaced at an angle or perpendicular to the longitudinal extension of the piston pin, on account of which the control element is also referred to as a control slider. A rotation of the piston pin relative to the piston can be effected or prevented by means of the control element.
In other words, when the control element is in the first position, depending on the rotational position of the piston pin, the control element effects a locking of the piston pin or a rotation of the piston pin relative to the piston. The compression ratio can thus optionally be maintained or changed.
In the piston arrangement according to the invention, the rotation of the piston pin relative to the piston and therefore the setting or adjustment of the compression ratio is preferably carried out as a result of centrifugal or inertial forces of the piston moving in the combustion chamber and/or as a result of pressure forces prevailing in the combustion chamber and acting on the piston. This provides a simple adjustment of the compression ratio without additional active actuating elements, which keeps the installation space required for the piston arrangement and the costs thereof low.
Further advantages, features and details of the invention are clear from the following description of a preferred embodiment and on the basis of the drawing. The features and combinations of features stated above in the description and the features and combinations of features stated below in the description of the drawings and/or shown in the drawings alone can be used not only in the combination specified in each case, but also in other combinations or in isolation without departing from the scope of the invention.